The Eigensystem Realization Algorithm for ambient vibration measurement using laser Doppler vibrometers

Laser Doppler vibrometers (LDVs) used in ambient vibration measurement have eliminated the expense of using sensors and exciters, and the need for a closing service of the structure during the measurement period. Since there are only two laser sources available for measuring responses at two points, the data acquired from all over the structure to provide information on its modal parameters will not be synchronous, leading to the fact that many current modal analysis identification techniques will not be applicable. Introduced in this paper is a technique to synchronize response measurements from the LDV, then feed them to the Eigensystem Realization Algorithm (ERA) to obtain the structure's modal parameters. Two experiments have been conducted on a steel plate to verify the technique. It has been found that the modal parameters can be successfully identified and that a change in these parameters is prominent when the system properties are changed. This finding is significant in structural health monitoring, in particular for damage detection, in that it can provide a fast, accurate, and relatively cheap routine to pinpoint the location of the damage.